The present application is directed to methods and devices for aligning media sheets in an image forming device, and more specifically to aligning the media sheets in an input tray.
Image forming devices, such as a color laser printer, facsimile machine, copier, all-in-one device, etc, move media sheets along a media path. The media sheets initially begin at an input tray that is sized to hold a stack of sheets. Each sheet is individually picked from the stack and introduced into the media path. The input tray may use side restraints to constrain and initially position the media sheets. Due to variability in loading the media sheets into the input tray, as well as dimensional tolerances in the media sheets and the input tray, all of the media sheets in the input tray may not be consistently and properly aligned. This may cause decreased feed reliability and skewing of the media sheets relative to the media path, which may result in print defects.
The movement of the media sheets from the input tray should occur without media jams and/or print defects. Media jams require the user to determine the location of the jam, access and remove the jammed sheet(s), and restart the image formation process. Print defects occur when the media sheet is not properly aligned when moving through the imaging area. Misalignment may occur in the scan directions (i.e., left and right), as well as the process directions (i.e., forward and backward).
A prior art input tray 10 is illustrated in FIG. 1. An input area 12 includes the support surface 15 sized to support the stack of media sheets 11 (not shown). A first side wall 13 extends vertically upward from the support surface 15. The first side wall 13 includes a reference surface 16. An edge of the media sheets 11 contacts the reference surface 16 to align the media sheets 11 in a proper orientation prior to feeding into the image forming device. A second side wall 17 extends vertically upward from the support surface 15 and is disposed opposite the first side wall 13. Located adjacent to the second side wall 17 is an adjustment plate 18. The adjustment plate 18 is movable along the support surface 15 by engaging a series of grooves 19 in the support surface 15. Moving the adjustment plate 18 in the scan direction along the grooves 19 varies a distance between the adjustment plate 18 and the reference surface 16 to accommodate a variety of media sheet 11 sizes.
The input tray 10 may also include a first end wall 20. As illustrated in FIG. 1, the first end wall 20 may be positionable at an angle to the support surface 15 to offset the stack at an angle to facilitate feeding the media sheets 11. First end wall 20 may also be movable in the feed direction to accommodate a variety of media sheet 11 sizes. The input tray 10 may also include a second end wall 21.
The input tray 10 may be inserted into the image forming device. Once inserted, a pick mechanism (not shown) may be positioned at the input area 12 to introduce the top-most media sheet 11 in the stack of media sheets 11 into the media feed path. Examples of image forming devices with pick mechanisms for introducing media sheets include Model C750 from Lexmark International of Lexington, Ky.
A function of the input tray 10 is to properly position the media sheets 11 so that each media sheet 11 is properly aligned with the media path. Improperly aligned media sheets 11 may misfeed when entering the media path, or may be skewed. One embodiment of a prior art device to align media sheets 11 in the media tray 10 is illustrated in FIG. 2. This embodiment includes a movable biasing side wall 18 that contacts an edge of the stack of media sheets 11. A biasing mechanism 32 such as a spring urges the biasing side wall 18 against the edge of the stack of media sheets 11, biasing the media sheets 11 against the reference surface 16 for proper alignment.
However, the size of the media sheets 11 may vary within a certain tolerance, and the media sheets 11 may not be placed consistently in the input tray 11. FIG. 2 illustrates how conditions such as these may cause an uneven edge 30 of the stack of media sheets 11. In this example, the biasing side wall 18 may contact an uneven section 30 of the edge, leaving gaps 31 between the biasing side wall 18 and the stack of media sheets 11. Without the biasing side wall 18 biasing the media sheets 11 near the top of the stack toward the reference surface 16, the top-most media sheet 11 may misfeed or skew when entering the media path.
The biasing side wall 18 illustrated in FIG. 2 may be constructed to have a sufficient biasing force to adequately bias a full stack of media sheets 11. When the stack of media sheets 11 is reduced and is near to being depleted, the remaining media sheets 11 will be subject to the full biasing force of the adjustment arm 11. While this force may be necessary when a full stack of media sheets 11 is present, the full biasing force may overwhelm the last remaining media sheets 11 and cause buckling or creasing of the media sheets. This may cause misfeeds or may damage the edge of the media sheets 11.